/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to you under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.calcite.util;

import java.io.Serializable;
import java.util.AbstractList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import javax.annotation.Nonnull;

/**
 * Code ported from Apache Calcite
 * org/apache/calcite/util/graph/Pair.java
 * Pair of objects.
 *
 * <p>Because a pair implements {@link #equals(Object)}, {@link #hashCode()} and
 * {@link #compareTo(Pair)}, it can be used in any kind of
 * {@link java.util.Collection}.
 *
 * @param <T1> Left-hand type
 * @param <T2> Right-hand type
 */
public class Pair<T1, T2>
        implements Comparable<Pair<T1, T2>>, Map.Entry<T1, T2>, Serializable {
    //~ Instance fields --------------------------------------------------------

    public final T1 left;
    public final T2 right;

    //~ Constructors -----------------------------------------------------------

    /**
     * Creates a Pair.
     *
     * @param left  left value
     * @param right right value
     */
    public Pair(T1 left, T2 right) {
        this.left = left;
        this.right = right;
    }

    /**
     * Creates a Pair of appropriate type.
     *
     * <p>This is a shorthand that allows you to omit implicit types. For
     * example, you can write:
     * <blockquote>return Pair.of(s, n);</blockquote>
     * instead of
     * <blockquote>return new Pair&lt;String, Integer&gt;(s, n);</blockquote>
     *
     * @param left  left value
     * @param right right value
     * @return A Pair
     */
    public static <T1, T2> Pair<T1, T2> of(T1 left, T2 right) {
        return new Pair<>(left, right);
    }

    /**
     * Creates a {@code Pair} from a {@link java.util.Map.Entry}.
     */
    public static <K, V> Pair<K, V> of(Map.Entry<K, V> entry) {
        return of(entry.getKey(), entry.getValue());
    }

    //~ Methods ----------------------------------------------------------------

    public boolean equals(Object obj) {
        return this == obj
                || (obj instanceof Pair)
                && Objects.equals(this.left, ((Pair) obj).left)
                && Objects.equals(this.right, ((Pair) obj).right);
    }

    /**
     * {@inheritDoc}
     *
     * <p>Computes hash code consistent with
     * {@link java.util.Map.Entry#hashCode()}.
     */
    @Override
    public int hashCode() {
        int keyHash = left == null ? 0 : left.hashCode();
        int valueHash = right == null ? 0 : right.hashCode();
        return keyHash ^ valueHash;
    }

    public int compareTo(@Nonnull Pair<T1, T2> that) {
        //noinspection unchecked
        int c = compare((Comparable) this.left, (Comparable) that.left);
        if (c == 0) {
            //noinspection unchecked
            c = compare((Comparable) this.right, (Comparable) that.right);
        }
        return c;
    }

    public String toString() {
        return "<" + left + ", " + right + ">";
    }

    public T1 getKey() {
        return left;
    }

    public T2 getValue() {
        return right;
    }

    public T2 setValue(T2 value) {
        throw new UnsupportedOperationException();
    }

    /**
     * Compares a pair of comparable values of the same type. Null collates
     * less than everything else, but equal to itself.
     *
     * @param c1 First value
     * @param c2 Second value
     * @return a negative integer, zero, or a positive integer if c1
     * is less than, equal to, or greater than c2.
     */
    private static <C extends Comparable<C>> int compare(C c1, C c2) {
        if (c1 == null) {
            if (c2 == null) {
                return 0;
            } else {
                return -1;
            }
        } else if (c2 == null) {
            return 1;
        } else {
            return c1.compareTo(c2);
        }
    }

    /**
     * Converts a collection of Pairs into a Map.
     *
     * <p>This is an obvious thing to do because Pair is similar in structure to
     * {@link java.util.Map.Entry}.
     *
     * <p>The map contains a copy of the collection of Pairs; if you change the
     * collection, the map does not change.
     *
     * @param pairs Collection of Pair objects
     * @return map with the same contents as the collection
     */
    public static <K, V> Map<K, V> toMap(Iterable<Pair<K, V>> pairs) {
        final Map<K, V> map = new HashMap<>();
        for (Pair<K, V> pair : pairs) {
            map.put(pair.left, pair.right);
        }
        return map;
    }

    /**
     * Converts two lists into a list of {@link Pair}s,
     * whose length is the lesser of the lengths of the
     * source lists.
     *
     * @param ks Left list
     * @param vs Right list
     * @return List of pairs
     */
    public static <K, V> List<Pair<K, V>> zip(List<K> ks, List<V> vs) {
        return zip(ks, vs, false);
    }

    /**
     * Converts two lists into a list of {@link Pair}s.
     *
     * <p>The length of the combined list is the lesser of the lengths of the
     * source lists. But typically the source lists will be the same length.</p>
     *
     * @param ks     Left list
     * @param vs     Right list
     * @param strict Whether to fail if lists have different size
     * @return List of pairs
     */
    public static <K, V> List<Pair<K, V>> zip(
            final List<K> ks,
            final List<V> vs,
            boolean strict) {
        final int size;
        if (strict) {
            if (ks.size() != vs.size()) {
                throw new RuntimeException();
            }
            size = ks.size();
        } else {
            size = Math.min(ks.size(), vs.size());
        }
        return new AbstractList<Pair<K, V>>() {
            public Pair<K, V> get(int index) {
                return Pair.of(ks.get(index), vs.get(index));
            }

            public int size() {
                return size;
            }
        };
    }

    /**
     * Converts two iterables into an iterable of {@link Pair}s.
     *
     * <p>The resulting iterator ends whenever the first of the input iterators
     * ends. But typically the source iterators will be the same length.</p>
     *
     * @param ks Left iterable
     * @param vs Right iterable
     * @return Iterable over pairs
     */
    public static <K, V> Iterable<Pair<K, V>> zip(
            final Iterable<? extends K> ks,
            final Iterable<? extends V> vs) {
        return new Iterable<Pair<K, V>>() {
            public Iterator<Pair<K, V>> iterator() {
                final Iterator<? extends K> kIterator = ks.iterator();
                final Iterator<? extends V> vIterator = vs.iterator();

                return new Iterator<Pair<K, V>>() {
                    public boolean hasNext() {
                        return kIterator.hasNext() && vIterator.hasNext();
                    }

                    @SuppressWarnings("unchecked")
                    public Pair<K, V> next() {
                        return (Pair<K, V>) Pair.of(kIterator.next(), vIterator.next());
                    }

                    public void remove() {
                        kIterator.remove();
                        vIterator.remove();
                    }
                };
            }
        };
    }

    /**
     * Converts two arrays into a list of {@link Pair}s.
     *
     * <p>The length of the combined list is the lesser of the lengths of the
     * source arrays. But typically the source arrays will be the same
     * length.</p>
     *
     * @param ks Left array
     * @param vs Right array
     * @return List of pairs
     */
    public static <K, V> List<Pair<K, V>> zip(
            final K[] ks,
            final V[] vs) {
        return new AbstractList<Pair<K, V>>() {
            public Pair<K, V> get(int index) {
                return Pair.of(ks[index], vs[index]);
            }

            public int size() {
                return Math.min(ks.length, vs.length);
            }
        };
    }

    /**
     * Returns an iterable over the left slice of an iterable.
     *
     * @param iterable Iterable over pairs
     * @param <L>      Left type
     * @param <R>      Right type
     * @return Iterable over the left elements
     */
    public static <L, R> Iterable<L> getLeft(
            final Iterable<? extends Map.Entry<L, R>> iterable) {
        return new Iterable<L>() {
            public Iterator<L> iterator() {
                final Iterator<? extends Map.Entry<L, R>> iterator =
                        iterable.iterator();
                return new Iterator<L>() {
                    public boolean hasNext() {
                        return iterator.hasNext();
                    }

                    public L next() {
                        return iterator.next().getKey();
                    }

                    public void remove() {
                        iterator.remove();
                    }
                };
            }
        };
    }

    /**
     * Returns an iterable over the right slice of an iterable.
     *
     * @param iterable Iterable over pairs
     * @param <L>      right type
     * @param <R>      Right type
     * @return Iterable over the right elements
     */
    public static <L, R> Iterable<R> getRight(
            final Iterable<? extends Map.Entry<L, R>> iterable) {
        return new Iterable<R>() {
            public Iterator<R> iterator() {
                final Iterator<? extends Map.Entry<L, R>> iterator =
                        iterable.iterator();
                return new Iterator<R>() {
                    public boolean hasNext() {
                        return iterator.hasNext();
                    }

                    public R next() {
                        return iterator.next().getValue();
                    }

                    public void remove() {
                        iterator.remove();
                    }
                };
            }
        };
    }

    public static <K, V> List<K> getLeft(
            final List<? extends Map.Entry<K, V>> pairs) {
        return new AbstractList<K>() {
            public K get(int index) {
                return pairs.get(index).getKey();
            }

            public int size() {
                return pairs.size();
            }
        };
    }

    public static <K, V> List<V> getRight(
            final List<? extends Map.Entry<K, V>> pairs) {
        return new AbstractList<V>() {
            public V get(int index) {
                return pairs.get(index).getValue();
            }

            public int size() {
                return pairs.size();
            }
        };
    }

    /**
     * Returns an iterator that iterates over (i, i + 1) pairs in an iterable.
     *
     * <p>For example, {@code adjacents([3, 5, 7])} returns [(3, 5), (5, 7)].</p>
     *
     * @param iterable Source collection
     * @param <T>      Element type
     * @return Iterable over adjacent element pairs
     */
    public static <T> Iterable<Pair<T, T>> adjacents(final Iterable<T> iterable) {
        return new Iterable<Pair<T, T>>() {
            public Iterator<Pair<T, T>> iterator() {
                final Iterator<T> iterator = iterable.iterator();
                if (!iterator.hasNext()) {
                    return Collections.emptyIterator();
                }
                final T first = iterator.next();
                return new Iterator<Pair<T, T>>() {
                    T previous = first;

                    public boolean hasNext() {
                        return iterator.hasNext();
                    }

                    public Pair<T, T> next() {
                        final T current = iterator.next();
                        final Pair<T, T> pair = of(previous, current);
                        previous = current;
                        return pair;
                    }

                    public void remove() {
                        throw new UnsupportedOperationException("remove");
                    }
                };
            }
        };
    }

    /**
     * Returns an iterator that iterates over (0, i) pairs in an iterable for
     * i &gt; 0.
     *
     * <p>For example, {@code firstAnd([3, 5, 7])} returns [(3, 5), (3, 7)].</p>
     *
     * @param iterable Source collection
     * @param <T>      Element type
     * @return Iterable over pairs of the first element and all other elements
     */
    public static <T> Iterable<Pair<T, T>> firstAnd(final Iterable<T> iterable) {
        return new Iterable<Pair<T, T>>() {
            public Iterator<Pair<T, T>> iterator() {
                final Iterator<T> iterator = iterable.iterator();
                if (!iterator.hasNext()) {
                    return Collections.emptyIterator();
                }
                final T first = iterator.next();
                return new Iterator<Pair<T, T>>() {
                    public boolean hasNext() {
                        return iterator.hasNext();
                    }

                    public Pair<T, T> next() {
                        return of(first, iterator.next());
                    }

                    public void remove() {
                        throw new UnsupportedOperationException("remove");
                    }
                };
            }
        };
    }
}

// End Pair.java
